The dynamic components of relational constructs should play an important role in driving performance. To take an initial step toward a theory of relationship dynamics, the authors introduce the construct of commitment velocity— or the rate and direction of change in commitment—and articulate its important role in understanding relationships. In two studies, the authors demonstrate that commitment velocity has a strong impact on performance, beyond the impact of the level of commitment. In Study 1, modeling six years of longitudinal data in a latent growth curve analysis, the authors empirically demonstrate the significance of commitment velocity as a predictor of performance. In Study 2, the authors use matched multiple-source data to investigate the drivers of commitment velocity. Both customer trust and dynamic capabilities for creating value through exchange relationships (i.e., communication capabilities for exploring and investment capabilities for exploiting opportunities) affect commitment velocity. However, trust and communication capabilities become less impactful as a relationship ages, while investment capabilities grow more important. The authors offer three post hoc tenets that represent initial components of a theory of relationship dynamics that integrates two streams of relationship marketing research into a unified perspective.